This section provides background information to facilitate a better understanding of the various aspects of the disclosure. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.
In the drilling, completing, or reworking of oil wells, a great variety of downhole tools are used. For example, but not by way of limitation, it is often desirable to seal tubing or other pipe in the casing of a well, such as when it is desired to pump cement or other slurry down the tubing and force the cement or slurry around the annulus of the tubing or out into a formation. In some instances, perforations in the well in one section need to be isolated from perforations in a second section of the well. Typically, the wellbore is lined with tubular or casing to strengthen the sides of the borehole and isolate the wellbore from the surrounding earthen formation. In order to access production fluid in a formation adjacent the wellbore, the casing is perforated, allowing the production fluid to enter the wellbore and be retrieved at the surface of the well. In other situations, there may be a need to isolate the bottom of the well from the wellhead. It then becomes necessary to seal the tubing with respect to the well casing to prevent the fluid pressure of the slurry from lifting the tubing out of the well or for otherwise isolating specific zones in which a wellbore has been placed. In other situations, there may be a need to create a pressure seal in the wellbore allowing fluid pressure to be applied to the wellbore to treat the isolated formation with pressurized fluids or solids. Downhole tools, referred to as packers and plugs, are designed for the aforementioned general purposes, and are well known in the art of producing oil and gas.
Traditional packers include a sealing element having anti-extrusion backup rings on both upper and lower ends and a series of slips above and/or below the sealing element. Typically, a setting tool is run with the packer to set the packer. The setting may be accomplished hydraulically due to relative movement created by the setting tool when subjected to applied pressure. This relative movement causes the slips to move cones up and extend into the surrounding tubular. At the same time, the sealing element may be compressed into sealing contact with the surrounding tubular. The set may be held by a body lock ring, which may prevent reversal of the relative movement. Additionally, a packer may be run into the wellbore as part of the liner string, which would be the case with a multi zone open hole frac (or fracturing) system.
The downhole isolation tool may be run in conjunction with other downhole tools, including, for example, a sleeve coupled to a ball seat, frac plugs, bridge plugs, etc. The downhole isolation tool may be set by wireline, coil tubing, or a conventional drill string. The tool may be run in open holes, cased holes, or other downhole completion systems. The downhole isolation tool and other downhole tools may be removed by drilling through the tool and circulating fluid to the surface to remove the drilled debris.
Existing sealing element anti-extrusion backup designs use three concepts, or a combination, to achieve containment of the element rubber during a high pressure pack-off at high temperature. The traditional designs include split rings, metal petal backup rings, and segmented backup rings.
Split ring element backup designs use two split rings with the scarf cuts opposed 180 degrees. Once the element setting pressure is applied, the rings expand radially outward and contact the casing inner diameter. Although the split section in the rings are opposed, and do not provide a continuous extrusion path, the width between the ends of the rings provide a significant volume for the element rubber to extrude into. This can decrease the rubber pressure in the element, limiting the sealing ability of the packer.
The metal petal design is a thin cup shaped ring that has been cut into petal segments on the outer diameter of the ring. When a compressive force is applied to the packer element during the setting procedure, the metal petals flex outwards and contact the casing wall. The petals trap the element rubber from extruding outwards past the clearance between the packer outer diameter and the casing inner diameter, due to the outward pressure on the petals from the element rubber and the friction between the petals and the casing inner diameter. While the overall extrusion gap has been limited by the petals, the gap between the petals created during the radial expansion becomes an extrusion gap for the element rubber. The metal petal concept can use multiple stacked metal petals to reduce the extrusion gap. Specifically, the cuts in the petal rings are offset so that there is no direct path for the rubber to extrude.
Another method used to limit sealing element extrusion is a segmented backup ring. This design uses a ring that has been cut axially on the outer diameter, segmenting the ring into small axial pieces. Usually the cuts have not been made completely through so the ring is still whole. Segmented backup rings have a tapered face and use a solid cone on the mandrel to push the segments radially outward during the setting process. When the packer setting pressure is applied, the ring is compressed against the cone. This breaks the segments into individual parts as they move to contact the casing inner diameter. Usually the segments are also guided as they expand so that the spacing between the segments will be equal. Multiple segmented rings can be offset so that no gap exists for the element rubber to extrude into. In certain applications, a combination of the metal petal and segmented ring design can be used to limit extrusion through the axial gaps created along the cuts when the segmented ring is compressed.